1. Field of the Invention
This invention concerns a time-triggered method and apparatus for the autonomous transmission of messages within a distributed real-time computer architecture. Such a computer architecture consists of a plurality of nodes. Each node has at least one communication control unit which is connected to a common communication channel shared by all notes. The communication is organized in rounds, where the structure and the attributes of a round are defined at a priori in a message descriptor list that specifies at which temporal position of the round a node has to send or receive a particular message.
This data transmission method is of particular interest to the automotive industry. There is an increasing tendency to replace electromechanical control devices within an automobile, such as an engine controller or a power window controller, by single-chip computer nodes. These single chip microcontrollers offer significant improvements in the cost/performance ratio and in the reliability over the devices they replace. The selection of the best interconnection technology between these nodes is a new challenge to the design engineer: On the one side there is the paramount concern for minimal production cost. This would suggest that a network based on a single wire bus as the preferred solution. On the other side there is an increasing concern for desirable system properties, such as composability in the temporal domain, testability, short error detection latency, dependability, and configuration flexibility. These system properties are determined to a large extent by the communication protocol that controls the information transfer between the different nodes.
2. Description of the Prior Art
According to the state of the art there exist many different methods for the transmission of messages in a distributed real-time computer system (see., e.g., the SAE paper J 2056/2--survey of known protocols, published in the 1994 SAE Handbook, Vol. 2, pp. 23273, Society of Automotive Engineers, Warrendale, Pa., 1994).
All of these published methods are event-triggered.
In an event-triggered method, the host computer has to generate an event that initiates the communication. A novel time-triggered method, where the activation of a message transmission is derived from the progression of time and not from an event generated by the host computer, for the autonomous transmission of messages in safety critical real-time applications is contained in the PCT Patent Application PCT/AT 93/00138 dated 4 September 1992.
Examples of analogous and non-analogous previously proposed message transmission systems are disclosed in the following U.S. and foreign patents:
______________________________________ Patentee ______________________________________ U.S. Pat. No. 4,168,469 Parikh, et al. 4,365,296 Ulmer 4,907,222 Slavik 5,001,642 Botzenhardt, et al. 5,208,807 Gass, et al. 5,303,347 Gagne, et al. 5,524,213 Dais, et al. 5,343,472 Michihira, et al. 5,355,368 Dore, et al. 5,537,549 Gee, et al. 5,553,308 Vink 5,555,548 Iwai, et al. PCT Published Patent Applications WO 9406080 Kopetz ______________________________________
It is an object of the present invention to provide a method for non-safety critical real-time applications that can be used on low cost microcontrollers and/or communication control units and to achieve high data efficiency combined with a short latency for the detection of message errors or node failures. It is another object of the present invention to provide a low cost apparatus for carrying out the new method.